1. Field
This application relates to airborne surveillance platforms.
2. Prior Art
There is a need for airborne platforms supporting electronic and optoelectronic sensors for gathering meteorological data and for transmitting images of the surrounding terrain in military, police and civil emergency applications
Crosby describes in U.S. Pat. No. 2,433,344 an aeronautic positioning device that automatically stabilizes a balloon, and airplane or a helicopter in a desired position above the earth, irrespective of wind and atmospheric conditions. The aerial vehicle supports a radio antenna of meteorological equipment. However, the positioning device is not suitable for maintaining a surveillance platform in a horizontal position since it relies solely on the aerodynamics of the supporting vehicle to meet this requirement. In order to ensure the stability of the image transmitted from a video camera or a thermal imager mounted on a platform, the latter has to remain horizontal or inclined at a fixed angle with respect to the horizontal plane.
Peterson teaches in U.S. Pat. No. 5,115,997 how an aerodynamic device helps to maintain a surveillance balloon elevation when exposed to high-velocity winds. The balloon is equipped with stabilizing fins and therefore always faces the prevailing wind. It supports a sensor pod containing a video camera and a thermal imager, as well as an azimuth actuator that allows a limited scan about the lubber line of the balloon. Consequently; the observation sensors cannot provide a full-circle view of the surrounding terrain. Furthermore, the sensor suite lacks a vertical control loop that would ensure a stable image to the operator.
An existing 4.9 m long surveillance balloon supports a 2-axis (pitch and roll), 3-gimbal gyro-stabilized platform equipped with a video camera and a thermal imager. The absence of yaw control precludes a full-circle scan of the surrounding terrain. It has also the disadvantage of being visible from afar and failing to operate in winds over 50 mph. It requires three technicians for its deployment and retrieval, and two for its operation. An advanced version of this surveillance system has a 3-axis (pitch, roll and yaw), 3-gimbal gyro-stabilized platform that ensures a full-circle observation capability. However, it has to be supported by a 15.6 m long balloon that requires three technicians for its deployment, operation and retrieval, and a large flat-bed trailer for transport.
Air surveillance and reconnaissance can also be accomplished by unmanned aerial vehicles (UAVs). A typical existing fixed-wing UAV has a wing span of 4.2 m and is powered by an electric motor. It is equipped with a gyro-stabilized platform that supports a video camera and a thermal imager. The UAV is launched from an all-terrain vehicle and is operated and recovered by two technicians. Piloting skills are required for controlling its flight and landing. Several man-portable rotary-wing and ducted-fan UAVs are being developed. Their main disadvantage is their tendency to drift and become unstable in crosswinds.
Surveillance from a high vantage point can also be achieved by mounting a video camera, a thermal imager and radar on a mast. Such an installation is presently used on a light armor reconnaissance vehicle (LAV-RECCE) that supports a 10-m telescoping mast. This surveillance system has the tactical disadvantage of operating only when the vehicle is stationary.